Intellectus. This word in St Thomas means sometimes the faculty
of 'understanding'; sometimes, as here, the act, or habit of
understanding, of which so much is made in modern philosophy under the
name of 'intuition.' St Thomas too makes much of it. Thus his
intellectus principiorum is 'intuition of first principles.' The
corresponding Aristotelian and Platonic word is nous as distinguished from dianoia. Kant's 'Reason' is his equivalent for
nous and intellectus.